In high-speed optical communications, a method of wavelength division multiplexing (DWDM) is used to increase transmission capacity of an optical fiber. A DWMD system comprises a plurality of transmission lasers, which operate at different wavelengths and are coupled to the same single-mode fiber. A wavelength of a laser should be stabilized within a narrow range corresponding to an optical transmission channel of the system.
The wavelength of the laser strongly depends on a temperature of a laser chip. The laser generally includes an internal wavelength locker measuring the wavelength of the laser and a temperature control circuit to compensate for temperature instability of the laser chip. Both the laser chip and the internal wavelength locker are typically disposed on a temperature-controlled submount maintained at a stabilized temperature independent from the environmental conditions.
However, in operation, there may be a need to modify a bias current of the laser chip to compensate for changes in the optical output power when, for example, the laser degrades over time. In this case, the wavelength locker's temperature also changes and the wavelength locker measures a wavelength of the laser with an error that may cause a cross-channel interference and, as such, limit the performance of the DWDM system.
Therefore, there is a need in the art for an improved method and apparatus for temperature stabilization of a wavelength of a laser used in a DWDM system.